1. Field of the Invention
The present invention relates to an active matrix substrate where thin film transistors are arranged in an array form, and an image display device using the active matrix substrate.
2. Background Art
In recent years, as image display devices, active matrix type liquid crystal displays, organic electroluminescence display devices, and electrophoretic display devices have been used.
Particularly, in the liquid crystal displays and the electrophoretic display devices, in order to display color images, color filters are generally used, and an image display element such as a liquid crystal layer or an electrophoretic particle layer is provided between an active matrix substrate on which semiconductor circuits are formed and a color filter substrate.
However, the image display device having such a structure has a problem in that since electrodes are not formed in a region where the TFTs (thin film transistors) are formed, a region for driven display elements is small, and an aperture ratio is low. In addition, in a case of the liquid crystal display, there is a problem in that a light leakage defect due to errors in position alignment between the active matrix substrate and the color filter substrate occurs, and a light blocking layer is formed to be large in order to give a margin to the errors in the position alignment for preventing the light leakage, and, as a result, an aperture ratio is lowered. In addition, in a case of the electrophoretic display device, a method of using micro-capsules as the electrophoretic particle layer is generally used, but a thickness of the micro-capsule layer is thick as 40 μm, and thus position alignment between the active matrix substrate and the color filter substrate is difficult, and a yield is low.
In order to solve the problem of the low aperture ratio, there is known an active matrix substrate having a configuration where an interlayer insulating layer is formed on the TFT, a pixel electrode is formed thereon, and a drain electrode and the pixel electrode are connected to each other via a through-hole portion provided at the interlayer insulating layer. Further, Japanese Patent No. 3383047 discloses a method in which an active matrix substrate having a COA (Color Filter On Array) structure where a color filter layer is formed on the TFT is used as a structure of the image display device using such an active matrix substrate, and thus errors in position alignment between the active matrix substrate and the color filter substrate is improved, thereby improving the aperture ratio. The active matrix substrate having the COA structure is provided with a through-hole at the color filter layer and the interlayer insulating layer in order to electrically connect the drain electrode and the pixel electrode.    Patent document 1: JP-B-3383047